(1) Field of the invention
The present invention relates to a paper feeder, and particularly to the paper feeder feeding a leading portion taken out of a rolled paper set in a container to a recording device. The present invention also relates to a printer, such as a thermal printer, equipped with the paper feeder.
(2) Description of the Related Art
A conventional paper feeder, a so-called throw-in-type paper feeder, is described in the Examined Japanese Patent Publication No. Hei 07-55746 (hereinafter referred to the JP' 746), in which, when an edge of paper taken out of a rolled paper set in a container is set to a recording section of a recording device and the paper is fed to print an image thereon, the paper can be continuously fed to the recording device while the rolled paper rotates such that it contacts front and rear walls of the container by a pulling force of the paper taken out during the rotation.
The conventional paper feeder includes a plurality of aligned support rollers rotatably provided at the bottom wall of the container to support the rolled paper such that the roll having a large diameter is supported at a rear position apart from a center of the roll by the rollers. This configuration may reduce torque of a motor to feed the paper from the roll having a large diameter, comparing with one that a roll having a large diameter is brought into contact with a bottom surface of a container without the support by rollers.
In the JP' 746 it is disclosed that friction force produced between the bottom wall of the container and the rolled paper is maintained constant, regardless of decrease in the diameter of the roll during its printing. According to the above construction, impact force is generated and applied to the paper at the recording section every time the paper is taken from the roll located in a stationary state, and thus causes deterioration of an image on the paper. However, no disclosure is present in the JP'746 as to a technology that prevents deterioration of the image on the paper caused by the impact force.
In the conventional paper feeder, the feeding speed of the paper when it is taken from the roll varies depending on an operational characteristic of the motor feeding the paper. More specifically, the motor reiterates start and stop every time the paper is fed to print thereon. Operational characteristic of the motor is composed of a slow-up period during which the number of rotations of the motor is increased gradually from a stationary state to a constant rotation, a constant rotational period during which the number of rotations is kept constant following the slow-up period, and a slow-down period during which the number of rotations is decreased gradually from the constant rotation to a stationary state. Therefore, speed of the paper fed fluctuates in response to the above-described operational characteristic.
At the slow-up period of the motor, stationary friction force produced by contacts both between the rolled paper in a stationary state and the bottom wall or the support rollers provided in the container and between the roll in the stationary state and the front wall of the container resists taking the paper from the roll. Since the paper feeder disclosed in the JP' 746 does not have any means that reduces the force for taking the paper from the roll, a stronger stationary friction force compared to a dynamic friction force acts as a relatively large feeding load against the take-out of the paper from the roll, and thus a smooth take-out of the paper from the roll can not be performed. As a result, the paper slides at the printing section instantaneously and thus it may cause unevenness in the printing pitch of images in the feeding direction.
Furthermore, after the slow-down period also, inertia attributed to rotation of the rolled paper tends to keep the rotation thereof although the motor stops. Therefore, the leading portion of the paper taken out of the roll may be apt to be taken out in excess because of the inertia.
When the paper is taken out of the roll subsequently to the above-described state in which the leading portion of the paper has been taken out in excess and has been loosed, the pulling force generated by the rotation of the motor is absorbed by the loosed portion of the paper and then makes a tension on the paper during the slow-up period of the motor. After that, the pulling force is suddenly effected to the rolled paper located in a stationary state and impact to the rolled paper is rapidly increased from the stationary state because of the rotation of the motor being increased. As a result, it becomes a high possibility that deterioration of printing is caused by unevenness in printing pitch of images in a feeding direction of the paper.
The conventional paper feeder does not include means for decreasing stationary friction force produced by a contact between the rolled paper and the front wall of the container. Therefore, when taking the paper from the roll, the stationary friction force causes an undesirable movement of the roll that the rolled paper goes up and down along the front wall for a moment. The fluctuation in position of the roll may cause the leading portion of the paper from the roll to be pulled back toward the roll, resulting in the deterioration of printing as described above.
Recently, rolled paper without a core is increasingly utilized in general to be exhausted to the end. When the roll having a small diameter resulting from the consumption receives the impact as described above, the roll may be apt to be deformed. As a result, deterioration of printing may occur in case that the rolled paper rotates intermittently in the container.
In addition, it is required in general more and more to increase the feeding speed of the rolled paper. The more the feeding speed increases, the more the impact applied to the leading portion of the rolled paper increases at the time that take-out of the paper from the roll begins. Therefore, the aforementioned problems arise remarkably.